parallelMap_parallelDo.js

const parallelMap = async (arr, f, n = Infinity, inPlace = false) => {
	const results = inPlace ? arr : Array(arr.length) 
	const entries = arr.entries()

	const worker = async () => {
		for (const [key, val] of entries)
			results[key] = await f(val, key)
	}

	await Promise.all(
		Array.from({length: Math.min(arr.length, n)}, worker)
	)

	return results
}

const parallelDo = async (arr, f, n = Infinity) => {
	const entries = arr.entries()

	const worker = async () => {
		for (const [key, val] of entries)
			await f(val, key)
	}

	await Promise.all(
		Array.from({length: Math.min(arr.length, n)}, worker)
	)
}

const delay = t => new Promise(r => setTimeout(r, t, t))

// test parallelMap
for (var n = 1; n <= 5; ++n) {
	const tid = `${n} workers`
	console.time(tid); console.log(await parallelMap(await [100, 200, 400, 800, 1600],delay, n)); console.timeEnd(tid)
}

// test parallelDo
for (var n = 1; n <= 5; ++n) {
	const tid = `${n} workers`
	console.time(tid); console.log(await parallelDo(await [100, 200, 400, 800, 1600],delay, n)); console.timeEnd(tid)
}